1. Field of the Invention
This invention generally relates to a control circuit and the method thereof, and more particularly, to a universal serial bus (USB, thereinafter called USB) control circuit and the method thereof that saves power.
2. Description of the Prior Art
FIG. 1 shows a connection of a control signal of a well-known USB control circuit. A control signal PdHsDRV is equal to the other control signal PdHsPort since both their physical lines are connected together. Wherein, the control signal PdHsPort is utilized to enable a USB device to keep working in high-speed actions while the USB device operates in high-speed mode (those skilled in the art also call “USB 2.0 mode”), and the control signal PdHsDRV is used to control the power of the transmitting module in the USB device. Accordingly, the power of the transmitting module in the USB device is always turned on as the USB device operates in high-speed mode.
However, in USB operation processes, the USB device may be in an idle status or may in a receiving status, and still, receiving and transmitting cannot be simultaneously performed in the same USB device. Therefore, it is not necessary to provide the power to the transmitting module when the USB device is idle or even is receiving data from another USB device. Also, from another aspect, as the USB device operates in high-speed mode whether is idle or is receiving data from another USB device, it bypasses a current (so-called leakage current) about 18 mA per second to the ground because the power of the transmitting module is still provided. This situation causes not only the leakage current but also a heating effect caused by the leakage current, and further, consumes the power of the USB device.
Taking a USB device, such as a portable USB digital camera that installs four batteries (double A, 1.5V, 1500 mAh) as its power source, as an example for further explanation, the USB device extra consumes over 1% power and further generates a heating effect about 59.4 mW (3.3V*18 mA=59.4 mW) per second while it is idle or it is receiving data from another USB device, such as a USB host, in high-speed mode. Herein, 3.3V represents the power voltage of the USB device. In other words, the power of the portable USB digital camera is consumed quite fast when the portable USB digital camera operates in high-speed mode but in an idle status or in a receiving status. However, the power for those portable USB devices (not only for USB digital cameras) is an important operation issue and should not be consumed too much in USB operations.
In view of the drawbacks mentioned with the USB control circuit in the prior art, there is a continued need to develop a new and improved control circuit and the method thereof that overcomes the disadvantages associated with the USB control circuit in the prior art. The advantages of this invention are that it solves the problems mentioned above.